Congestion monitoring of mobile entities

ABSTRACT

A method, by a policy control unit of a mobile communications network, to control a signaling of congestion information of mobile entities at a plurality of congestion monitoring units that monitor which mobile entities are affected by a congestion state in a radio access network of the mobile communications network. The method comprises receiving, from one of the congestion monitoring units, an indication that one of the mobile entities is affected by a congestion state, storing said one congestion monitoring unit from which the indication is received as the current congestion monitoring unit for said one mobile entity, receiving, from another congestion monitoring unit, the indication that said one mobile entity is affected by a congestion state, and indicating, in response to the indication received from the other monitoring unit, to the current congestion monitoring unit a release of congestion information relating to said one mobile entity.

TECHNICAL FIELD

The present invention relates to a method, by a policy control unit of amobile communications network, to control a signaling of congestioninformation of mobile entities and to the corresponding policy controlunit. The invention furthermore relates to a method of operating acongestion monitoring unit which monitors which mobile entities areaffected by a congestion state in a radio access network of a mobilecommunications network and to the corresponding congestion monitoringunit. The invention furthermore relates to a computer program, to acomputer program product and to a corresponding carrier containing thecomputer program.

BACKGROUND

Packet data traffic is growing very quickly in mobile communicationsnetworks or mobile operator networks, in many cases it grows much fasterthan the rate at which the operator can expand its network capacity.This leads to more frequent occurrences of network congestion when theoffered traffic is higher than what the RAN (radio access network) isable to fulfill. Also, new services appear often, which may lead to asituation when a new QoE (Quality of Experience) requirement has to beintroduced into the network quickly. In this situation, operators needefficient and flexible tools by which they can control how thebottleneck RAN capacity can be best shared so that they can maximize theQuality of Experience of their users.

Recently, in the context of the 3GPP UPCON (User plane congestionmanagement) work item, a new type of solution has been put forward whichutilizes congestion feedback from the CN (Core Network) to the RAN. Thishas been documented in 3GPP TR 23.705 version 0.10.0. When RAN indicatescongestion to the CN, it can take actions to mitigate the congestion,such as limiting some classes of traffic, or request to delay some otherclasses of traffic.

The RAN OAM (Operation and Maintenance) systems contain a lot ofinformation based on which an operator may derive when a state ofcongestion takes place. Such information can include for example dataabout the amount of packet loss, packet delay, traffic throughput, airinterface utilization, number of connected users, number of connectedusers with non-empty buffers, etc. A mobile network operator mayconfigure thresholds on one or on a combination of these metrics todetermine when a state of congestion is considered in its network. It isalso possible for a mobile operator to define multiple levels ofcongestion using the combination of these metrics, so that thecongestion mitigation actions can correspond to the current level ofcongestion.

Current RAN OAM systems work on a per cell or lower spatial granularity.That means that the determination of congestion could be performed on aper cell basis, or for a group of cells (such as cells belonging to thesame eNB (eNode B) for LTE (Long Term Evolution), or cells belonging tothe same Service Area for 3G). In order for the core network to takeappropriate mitigation action, the core network also has to find outwhich UEs (User Equipments/mobile entities) are located in a given cell.Hence, the list of affected UEs needs to be determined for the cellswhich are considered congested based on OAM data.

One solution for OAM based congestion reporting is documented insolution 1.5.5 (also called off-path solution) in section 6.1.5.5 of3GPP TR 23.705, which suggests a new interface Nq for this purpose. TheNq interface is defined between a new network entity RCAF (RANCongestion Awareness Function) and the MME (Mobility Management Entity).The RCAF is the node which is assumed to receive RAN congestion relateddata from the RAN OAM system on a per cell (or lower) spatialgranularity. Then, using the Nq interface, the RCAF queries the MME tosupply the list of UEs per cell.

A similar approach is suggested for the 3G case, using Nq′ interfacefrom the RCAF to the SGSN (Serving GPRS Support Node). However, there isa difference for 3G since the RAN can already have the UE identities, asthe IMSI (International Mobile Subscriber Identity) can be sent to theRNC (Radio Network Controller) node. The RAN OAM collects these IMSIsand RAN OAM then supplies the list of UEs identified by IMSI thataffected by congestion to the RCAF. Hence, for 3G it is suggested thatthe list of UEs affected by congestion are known to the RCAF withoutcontacting the SGSN over the Nq′ interface.

Once the RCAF node has collected information about the set of UEsaffected by congestion, it notifies the PCRF (Policy and Charging RulesFunction) about the congestion level of the affected UEs (identified bya UE identifier such as the IMSI (International Mobile SubscriberIdentity)). The Np interface is defined between the RCAF and the PCRFfor this purpose. As described in TR 23.705, the PCRF can then takeactions to mitigate the congestion e.g., by limiting the traffic in anenforcement node (PGW or TDF) (Packed Gateway or Traffic DetectionFunction), or notifying the application function (AF) to limit or delaythe traffic, etc.

One problem with the congestion notifications from the RCAF to the PCRFis the handling of the UE mobility. There may be multiple RCAF nodes ina network, each corresponding to a certain geographical area. It mayalso be possible that a given RCAF handles a single RAT (radio accesstechnology) type only, such as LTE only or 3G only, and the UE may movebetween the RATs. As a result of UE mobility between different RCAFs,the PCRF may receive notifications from multiple RCAFs for a given UE,and it may not be always possible to know which is the latestinformation.

This is complicated by additional factors. Firstly, the RCAF may getperiodic information about UEs on a longer time-scale, such as 15 mins,and consequently the RCAF may perform the reporting to the PCRF onlyafter some delay. Different RCAFs are not synchronized, so it may happenthat when the UE moves from RCAF1 to RCAF2, the reporting from RCAF2takes place earlier than from RCAF1. Hence the ordering of the incomingcongestion notifications at the PCRF may not reflect the ordering of UEmobility events.

Secondly, the RCAF may only know about a given UE if it is affected bycongestion. For a UE that is not affected by congestion, the RCAF maynot get information for that given UE via OAM or via Nq. Therefore itmay happen that the UE moves from RCAF1 to RCAF2, the UE is affected bycongestion at RCAF1 but not affected by congestion at RCAF2 hence RCAF2does not produce any congestion indication to the PCRF. This may lead tothe PCRF incorrectly believe that the UE experiences congestion atRCAF1.

One additional aspect to consider in the solution of these problems isthat the signaling load on the Np interface between the RCAF and thePCRF may be significant. There may be a high number of UEs in a network,and it is possible that the congestion state changes for a substantialfraction of the UEs. Hence it is desirable to limit the signaling loadon the Np interface.

The following solution approaches for UE mobility handling have beensuggested.

Approach 1. In 3GPP TR 23.705 version 0.10.0, a validity time isassociated with the information sent from the RCAF to the PCRF on the Npinterface. It is stated that “When this time has elapsed and no furthercongestion information has been received, the congestion is assumed tobe over.” Such a validity time can be used in the PCRF to prevent thatthe PCRF permanently assumes the UE to be affected by congestion whileit has moved to another RCAF where it is not affected by congestion.

Approach 2. In protocols handling mobility, it is common to usetimestamps to signal the ordering of the events in the receiving node.E.g., timestamps can be used as one of the options in the PMIPv6mobility protocol (RFC 5213 from August 2008).

Approach 3. In protocols handling mobility, it is also common to usesequence numbers to signal the ordering of the events in the receivingnode. E.g., sequence numbers can be used as one of the options in thePMIPv6 mobility protocol (RFC 5213).

Approach 4. Intra-LTE TAU (Tracking Area Update) and Inter-eNodeBHandover with Serving GW (Gateway, SGW) Relocation procedure with PMIP(Proxy Mobile IP)-based S5 interface is defined in 3GPP TS 23.402version 12.4.0, section 5.7.1. That procedure includes the Gxc session(i.e., GW control session) moved from an old SGW to a new SGW. That Gxcsession is terminated in the PCRF, in that way the scenario is similarto mobility handling at the Np interface since the endpoint is the PCRF.

Approach 5. In signaling procedures between the MME and the HSS (HomeSubscriber Server) for mobility (see e.g., 3GPP TR 23.401 version12.4.0, section 5.3.3.1 describing the TAU procedure), the HSS sends aCancel location to the old MME when it receives a mobility update(Update location) from a new MME. This is used to release some of thecontext information in the old MME.

The following problems are seen with the existing solutions describedabove.

Approach 1. Using a validity time would be useful if the congestion endsjust when the validity time expires. However, if the congestion ends atsome other time compared to when the validity timer expires, thisapproach does not perform well. In case the congestion ends sooner thanthe validity timer expires, we maintain CN throttling actionsunnecessarily, degrading the end user performance. In case thecongestion ends later than the validity timer expires, new signaling isnecessary to maintain the CN action, which can lead to excessive andunnecessary signaling. Given that the length of the congestion periodcannot be accurately predicted in advance, these issues are expecteddegrade the performance of this solution.

Note also that the congestion status may change between differentlevels, and those changes are not handled by validity timers which onlyconsider the transition to no congestion state. Hence, the gainpotential of the validity timer approach is very limited, and the riskof performance loss is higher.

An additional problem with validity timer based approach is that thePCRF may receive congestion information from more than one RCAF nodesand it is possible that there are multiple such congestion informationwhose validity timer has not yet expired. In that case, it isproblematic for the PCRF to determine which is the actual congestionlevel. Some heuristics need to be used (use the average; or maximum; oruse the latest received information), but such heuristics might not beefficient.

Note also that the use of validity time impacts the PCRF since the PCRFnode is otherwise not timer-based.

Approach 2. The use of timestamps in our case is problematic. On the onehand, there is no timing synchronization between the RCAF nodes. Buteven if we could use sufficiently accurate timing information, it wouldnot be sufficient, due to the long and unpredictable delay in the OAMbased data reporting. As noted earlier, it is possible that the UE movesfrom RCAF1 to RCAF2, yet the congestion information reporting takesplace from the RCAF2 earlier than from RCAF1. As the RCAF uses longtime-scale OAM reporting (such as reporting on a 15 mins period), theRCAF has no way to determine the whereabouts of a UE on a shorter timescale. So the time ordering of the signaling messages from RCAF nodes toPCRF is not sufficient to determine the ordering of UE mobility events.

Approach 3. Sequence numbering is not applicable in our case, becausethere is no way to transfer sequence number state from RCAF1 to RCAF2.That is because each RCAF acts on its own, and a RCAF has no way todetermine which was the previous RCAF in case of mobility, or which willbe the next RCAF in case the UE moves. Hence it is not possible toestablish any communication between RCAF1 and RCAF2 to transfer stateinformation for the current sequence numbering.

Approach 4. The solution for Approach 4 involves the explicitestablishment of a new Gxc session between the new SGW and PCRF, and theexplicit release of the old Gxc session between the old SGW and PCRF.The procedure guarantees that the establishment of the new sessionalways takes place, and the release of the old session also always takesplace. This is possible since the procedure involves explicit contexttransfer from an old MME to a new MME which in turn control theestablishment and release of the sessions between the SGWs and the PCRF.(If the MME does not change, the same MME can control the sessionestablishment and release between the SGWs and the PCRF.) This approachis not applicable in our case because there is no context transfer orsingle node which can control both the RCAF1 and RCAF2 at mobility.Further, in our case a new RCAF may not detect a UE if it is notexperiencing congestion, so it cannot make sure that a new session tothe PCRF is always established.

Approach 5. In existing mobility procedures between the MME and the HSS,the HSS sends a Cancel location message to the old MME unconditionally.That is possible since there is a context transfer between the new andold MME which guarantees that an indication from the new MME is alwayssent to the HSS. In our case, such a message to release the old contextfrom the PCRF to the old RCAF cannot be always sent, because there is noguarantee that the new RCAF will signal to the PCRF. Furthermore, it isnot possible to send such a message unconditionally, because it ispossible that an RCAF node indicates to the PCRF about change to the nocongestion state.

SUMMARY

Accordingly, a need exists to overcome at least some of theabove-mentioned problems and to provide a possibility to provide correctcongestion information for a mobile entity in an effective way, whileminimizing a signal exchange between the affected nodes in the network.

This need is met by the features of the independent claims. Thedependent claims describe further embodiments.

According to a first aspect, a method is provided, carried out by apolicy control unit of a mobile communications network to control asignaling of congestion information of mobile entities at a plurality ofcongestion monitoring units which monitor which mobile entities areaffected by a congestion state in a radio access network of the mobilecommunications network. The method comprises the steps of receiving,from one of the congestion monitoring units, a first indication that oneof the mobile entities is affected by a congestion state. Said onecongestion monitoring unit from which the first indication is receivedis stored as the current congestion monitoring unit for said one mobileentity. Furthermore, the first indication is received from anothercongestion monitoring unit that said one mobile entity is affected by acongestion state. In response to the first indication received from theother monitoring unit, it is indicated to the current congestionmonitoring unit to release congestion information relating to said onemobile entity. In other word, the policy control unit indicates to thecurrent congestion monitoring unit to stop congestion reporting relatingto said mobile entity.

The invention furthermore relates to the corresponding policy controlnode which operates as discussed above and controls a signaling forcongestion information at a plurality of congestion monitoring units.The policy control unit comprises a receiver configured to receive fromone of the congestion monitoring units a first indication that one ofthe mobile entities is affected by a congestion state. A database isprovided which is configured to store said one congestion monitoringunit from which the first indication is received as the currentcongestion monitoring unit for said one mobile entity. Furthermore, thepolicy control unit comprises a transmitter and a processing unitwherein, when the receiver receives the first indication that said onemobile entity is affected by a congestion state from another congestionmonitoring unit, the processing unit is adapted to indicate by thetransmitter, to the current congestion monitoring unit to releasecongestion information relating to the one mobile entity in response tothe received first indication.

The policy control unit can work as described above and the policycontrol unit may be a PCRF.

The invention furthermore relates to a method to operate a congestionmonitoring unit which monitors which mobile entities are affected by acongestion state in a radio access network of a mobile communicationsnetwork. The congestion monitoring unit receives, from a policy controlunit of the mobile communications network, an indication to releasecongestion information relating to said one mobile entity. Thecongestion monitoring unit then releases the congestion information forsaid one mobile entity in response to the received indication. Theinvention furthermore relates to the corresponding congestion monitoringunit. Furthermore, the invention provides a computer program comprisinginstructions which, when executed on at least one processing unit, causethe processing unit of the congestion monitoring unit or the policycontrol unit to carry out the method as described above. The inventionfurthermore provides a computer program product comprising the computerprogram and a carrier containing the computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofembodiments given in conjunction with the accompanying drawings.

FIG. 1 shows a system architecture incorporating features of theinvention including a congestion monitoring unit and a policy controlunit which interact to effectively signal congestion information.

FIG. 2 is a schematic block diagram of a policy control unit shown inFIG. 1.

FIG. 3 is a schematic block diagram of a congestion monitoring unitincorporating features of the invention and shown in FIG. 1.

FIG. 4 shows a message exchange between a policy control unit anddifferent congestion monitoring units which can effectively cope withthe scenario in which a mobile entity moves from the coverage of onecongestion monitoring unit to another congestion monitoring unit.

FIG. 5 shows a message exchange between a congestion monitoring unit andthe policy control unit when the policy control unit determines that adata packet session of a mobile entity has terminated.

FIG. 6 shows a flowchart including the steps carried out at a policycontrol unit to handle congestion information when the mobile entity hasmoved from the control of one congestion monitoring unit to the controlof another congestion monitoring unit.

FIG. 7 shows a flowchart comprising the steps carried out at the policycontrol unit when one of the congestion monitoring units provides theinformation that a mobile entity is in a non-congested state.

FIG. 8 shows a flowchart including the steps carried out at thecongestion monitoring unit when receiving a message to releasecongestion information of a mobile entity.

DETAILED DESCRIPTION

In the following, concepts according to embodiments of the inventionwill be explained in more detail by referring to the accompanyingdrawings.

A policy control unit stores the last congestion monitoring unit foreach mobile entity and if a congestion state is received from a newcongestion monitoring unit for one mobile entity, the old congestionmonitoring unit is informed to stop congestion reporting for said onemobile entity.

This means that the congestion monitoring unit reports the changes inthe congestion state and the policy control unit maintains the currentcongestion monitoring unit which has last indicated that the mobileentity is affected by a congestion. An explicit signaling is used inwhich the policy control unit informs the current congestion monitoringunit, which is then an old congestion monitoring unit, as the firstindication is then received from another congestion monitoring unit, torelease the congestion information stored at the current congestionmonitoring unit. This especially helps to avoid errors occurring withcongestion information stored at old congestion monitoring units.Especially when the mobile entity moves from the responsibility of onecongestion monitoring unit to another congestion monitoring unit, theabove discussed method provides advantages. The policy control unit thenindicates to stop the congestion reporting until said one mobile entitybecomes affected by a congested state once again. The policy controlunit maintains the current congestion monitoring unit which has lastindicated that the mobile entity is affected by a congestion and when anew or another congestion monitoring unit indicates that the mobileentity is affected by congestion, the policy control unit informs thecurrently stored congestion monitoring unit to explicitly release anyinformation relating to said one mobile entity.

It is possible that a second indication is received from any of theplurality of congestion monitoring unit that said one mobile entity isnot affected by a congestion state. In this situation, the secondindication is then ignored and no indication is sent to the currentcongestion monitoring unit to release congestion information for saidone mobile entity.

The policy control unit does not take into account this secondindication. The current congestion monitoring unit remains unchanged.The policy control unit assumes the previously determined congestionstatus without updating it to a non-congestion state. This ignoring ofthe policy control unit helps especially to improve the situation when amobile entity has moved from the responsibility area of one congestionmonitoring unit to the area of another congestion monitoring unit. Ifthe first congestion monitoring unit then indicates a non-congestedstate, even though it does not know whether a congested state is presentat the other congestion monitoring unit in the area where the mobileentity is now located. The fact that the policy control unit ignores thesecond indication of a non-congested state helps to avoid the policycontrol unit to take over a wrong congestion state. The currentcongestion state may be kept as the current congestion state when thesecond indication is received in which any of the congestion monitoringunits indicated that the mobile entity is currently not affected by acongestion state, i.e. is in a non-congested state.

The policy control unit may furthermore store the other congestionmonitoring unit from which the first indication is received that themobile entity is affected by a congestion state. This means that when aninformation about a congested state for one mobile entity is receivedfrom a congestion monitoring unit, this congestion monitoring unit isthen stored as the current congestion monitoring unit for said mobileentity. However, as mentioned above, when in indication about anon-congested is received from one of the congestion monitoring units,this congestion monitoring unit is not stored as the current congestionmonitoring unit.

Furthermore, it is possible that when a termination of a data packetsession of said mobile entity is detected, it is indicated to thecurrent congestion monitoring unit to release congestion informationrelating to said mobile entity. By way of example, when the policycontrol unit removes its own congestion information at the terminationof a data packet session, e.g. the mobile entity is being detached, thenthe policy control unit explicitly signals to the current congestionmonitoring unit to release the congestion information relating to saidone mobile entity.

The step of indicating a release of congestion information can containinformation to release a context for the one mobile entity.

When the second indication is received by the policy control unitindicating that said mobile entity is not affected by a congestionstate, an acknowledgement can be transmitted as a response to thecorresponding congestion monitoring unit which transmitted the secondindication. Even though the policy control unit does not react to thisinformation about the non-congested state, nevertheless anacknowledgement is transmitted back as a response. This helps to avoidthe situation that, if no acknowledgement were sent that the secondindication about the non-congested state, the second indication is sentseveral times as the congestion monitoring unit may deduce from amissing acknowledgement that the indication was not correctly receivedand that the indication is to be transmitted a second time.

Furthermore, the plurality of congestion monitoring units may beinformed whether or not a monitoring of the congestion state should becarried out for said one mobile entity. Here, the policy control unitcan determine whether the monitoring of a congestion state should beenabled or disabled. When the reporting of the congestion state isenabled, the policy control unit can furthermore inform the plurality ofcongestion monitoring units that the congestion state should only bereported to the policy control unit when the congestion state hasreached a pre-defined level or a pre-defined level range. In thisembodiment, the policy control unit can implement reporting restrictionsin the congestion monitoring units and the congestion monitoring unitcarries out the monitoring of a congestion state in accordance with theabove received information, i.e. it may only report a congested statewhen a pre-defined level of congestion or a pre-defined level range ofcongestion is detected. If the mobile entity is not above the predefinedlevel or within the predefined level range, a non-congested state may befollowed in which the congestion monitoring unit issues a secondindication indicating a non-congested state.

FIG. 1 shows an architecture in which a congestion monitoring unit suchas a RCAF 200 (RAN congestion awareness function) determines congestionstates of mobile entities (not shown) in a radio access network 10. TheRCAF 200 is able to determine a RAN user plan congestion which occurswhen the demand for RAN resources exceeds the available RAN capacity todeliver user data for a period of time. RAN user plan congestion leadsinter alia to packet drops or delays. The RCAF 200 collects inter aliathe ongoing RAN user plane performance status at cell level from the RANOAM (Operation and Maintenance) unit 11 which is further assembled priorto reporting it to a policy control unit such as a Policy and ChargingRules Function (PCRF) 100. For the communication of congestioninformation between RCAF 200 and PCRF 100, an Np interface is provided.

The RCAF 200 is furthermore connected via an Nq/Nq′ interface to MME orSGSN 20. The user plane data, the congestion of which is monitored, istransmitted from RAN 10 via a serving gateway, SGW 30, which rules andforwards user data packets to a PDN (Packet Data Network) gateway 40.From the PDN gateway 40, the user data are transmitted via a trafficdetection function (TDF) 50 to the packet data network, PDN 60.

The following description focuses on RCAF 200 or a quantity of RCAF 200and PCRF 100 and the interacting between these entities as the mainaspects of the invention are related to these functional entities.

The following principles are used by the RCAF 200 and the PCRF 100 tooptimize the monitoring of congestion information of mobile entities,especially when a mobile entity moves from an area in which one RCAFdetermines the congestion state of the radio access network to anotherRCAF which determines the congestion state of the mobile entities inanother area. In the embodiment of FIG. 1, one RCAF 200 is shown.However, it should be understood that different RCAFs 200 are providedin the mobile communications network which is partly shown in FIG. 1.The RCAF 200 uses the information provided by the RAN OAM 11 such as theamount of data packet loss, packet delay, traffic throughput, airinterface utilization or number of connected users and can thendetermine, based on configurable thresholds, a congestion state of acertain area. The RCAF 200 determines the mobile entities affected by acongestion state in an RAN area using information provided by MME or bySGSN 20.

The following principles are used by the RCAF 200 and the PCRF 100 todetermine directly whether a mobile entity is affected by a congestionstate or not.

-   -   The RCAF 200 reports the changes in the congestion state        including both changes to a congestion state and changes to a        non-congested state.    -   The PCRF 100 maintains the current RCAF which has last indicated        that a mobile entity is affected by congestion.    -   When a new or another RCAF 200 indicates that the mobile entity        is affected by congestion, the PCRF 100 sends a message to the        old RCAF to explicitly release congestion information relating        to said mobile entity, i.e. to release a context at the old        RCAF.    -   When the PCRF 100 receives a message from a new RCAF 200, which        could be any of the RCAFs, indicating that the mobile entity is        not affected by congestion, this message is not taken into        account at the PCRF 100.    -   When the PCRF 100 removes its own UE context at IP-CAN session        termination, e.g. the UE is being detached, the PCRF 100        explicitly signals to the current RCAF 200 to release the UE        context.    -   The RCAF 200, when indicated by PCRF signaling, then releases        the context of the mobile entity.

In the following, based on examples, it will be explained why theabove-mentioned principles help to improve the correct detection of acongestion state of a mobile entity.

The RCAF 200 gets information about the congested cells and the UEsaffected by congestion based on OAM data and with the help of the Nqinterface. When a UE is not affected by congestion, the RCAF nodes donot have any information about the given UE. Therefore when the RCAF 200detects that a given UE which was earlier affected by congestion is nolonger affected by congestion, the RCAF 200 node itself cannot determinewhether this is because the UE has moved to another RCAF, or this isbecause the congestion has ceased at the UE's current location. The RCAF200 may indicate to the PCRF that a UE does not experience congestion atthe given RCAF, but this does not rule out the possibility that anotherRCAF may indicate that the same UE is affected by congestion.

Similarly, when RCAF 200 detects that a new UE is affected bycongestion, it cannot determine whether the UE has moved in from anotherRCAF, or whether congestion has started at the UE's current location, orwhether the UE has moved to a congested area, or whether the UE has beenswitched on at a congested area. For these reasons, there cannot be anyhandover procedure with context transfer from an old RCAF to a new RCAF.

Hence we can draw the following conclusions for mobility handling.

Conclusion 1: An RCAF 200 node cannot differentiate whether a UE that isno longer affected by congestion has moved to another RCAF or not.

Conclusion 2: When RCAF 200 indicates no congestion to the PCRF 100 fora given UE on the Np interface, this should be interpreted as nocongestion experienced at the given RCAF which does not exclude thatanother RCAF may report that the same UE experiences congestion.

Conclusion 3: There cannot be any handover procedure from an old RCAF toa new RCAF involving context transfer.

The invention uses the principle that the RCAF 200 reports the changesin the congestion state such that it can avoid reporting the same stateagain and again. In this way, the signaling load can be reduced and avalid timer on the Np interface can be avoided.

Additionally, the concept of dynamic reporting policies or in otherwords reporting restrictions is possible. Such reporting restrictionscan be defined on a per UE basis, and can control whether or notcongestion reporting is enabled for a given UE; and which congestionlevels should be reported when reporting is enabled. It is possible toavoid reporting certain congestion levels by defining one or more setsof congestion levels, such that the RCAF indicates only that the UEexperiences a congestion level within the given set but does notindicate the congestion level itself. A set can typically contain arange of congestion levels. E.g., set#1={“no congestion”, level 1congestion}, and set#2={level 2 congestion, level 3 congestion}; andthen the RCAF only indicates whether the UE experiences a congestionlevel in set#1 or set#2. (The sets must be non-overlapping such that agiven congestion level can belong to a single set only.)

Such reporting restrictions can be realized by signaling from the PCRF100 to the RCAF node 200 over the Np interface. In this way, an operatorcan avoid unnecessary signaling, e.g. in the case of a user with premiumsubscription which is not going to be subject to congestion mitigationrules; or similarly for machine type devices with small data for whichthere is no need to install mitigation rules due to low traffic.

In the following, the context of a mobile entity stored at RCAF 200 willbe discussed. The UE, by entity context at the RCAF 200, refers to thedata that needs to be stored at the RCAF 200 and is specific to a givenUE. The following information may be included in the UE context at theRCAF 200.

To clarify the UE handling in the RCAF 200 the information that needs tobe stored in the PCRF 100 is stored on a per UE basis.

-   -   The previously reported congestion level for a given UE. This        needs to be stored so that the RCAF 200 can determine when a        change has taken place in the congestion level. This enables        delta reporting on the Np interface which reduces the signaling        load.    -   The reporting restrictions discussed above received from the        PCRF 100 are stored in the RCAF 200 on a per UE, per APN basis        so that they can be subsequently applied on the Np interface.        After the RCAF 200 has determined whether the congestion level        for a given UE has changed, it checks the related reporting        restrictions if they exist. The change in the congestion level        is only indicated to the PCRF 100 if allowed by the reporting        restrictions.

The UE context is kept in a given RCAF 200 only, and there is no contexttransfer between RCAFs. The context is created in the RCAF 200 when itis first determined in an RCAF 200 that a UE is affected by congestion,or when reporting restrictions are sent from the PCRF 100 removed in theRCAF 200 when explicitly indicated by the PCRF 100 using signaling onthe Np interface. The context may also be removed from the RCAF 200 incase the UE has no reporting restrictions and the UE does not experiencecongestion this has already been reported to the PCRF 100.

Other information may also be included in the UE context at the RCAF200.

In the following, different mobility scenarios of mobile entities arediscussed in which the above-mentioned basic principles at the RCAF 200or the PCRF 100 help to determine the correct mobility information.

In light of the conclusions 1, 2 and 3 above, the mobility handling onthe Np interface has to work without any direct signaling andco-ordination between the old and new RCAF nodes 200. In most cases, UEmobility from an old RCAF to a new RCAF is solved automatically: whenthe UE becomes affected by congestion at a new RCAF, it triggerscongestion reporting on Np for the given UE which automatically makesthe PCRF 100 aware of the identity of the new RCAF. However, there canbe problematic cases as follows.

-   -   Scenario 1. UE is affected by congestion at a first RCAF, named        RCAF1 hereinafter and then moves to another RCAF, named RCAF2        hereinafter, where it is also affected by congestion.        Consequently RCAF2 indicates the congestion situation to the        PCRF. RCAF1 detects that the UE is no longer affected by        congestion, and reports that fact to the PCRF. This information        may arrive to the PCRF later than the reporting from RCAF2,        since the timing of the signaling is not synchronized between        RCAF1 and RCAF2. If the PCRF considers this later signaling from        RCAF1, it would incorrectly consider the UE as not congested.    -   Scenario 2. UE is affected by congestion at RCAF1 and then moves        to RCAF2 where it is also affected by congestion. Soon after        that, the UE moves back to RCAF1 where it experiences the same        level of congestion as before. Both RCAF1 and RCAF2 detect that        the UE is affected by congestion. RCAF2 indicates the congestion        to the PCRF which indicates the mobility to RCAF2. But RCAF1        does not signal to the PCRF because the congestion status at        RCAF1 has not changed. This makes the PCRF incorrectly believe        that the UE is located at RCAF2 and experiences the congestion        level as reported by RCAF2, while in fact the UE has moved back        to RCAF1 and experiences the congestion level as reported by        RCAF1 earlier.

To solve these problematic scenarios, it is proposed to use explicitsignaling from the PCRF 100 to release the UE context at the old RCAF.This avoids the problems due to having obsolete UE contexts stored atold RCAF nodes, and thereby avoids the problems with the abovescenarios. The solution involves additional signaling during mobility;this is assumed to be acceptable, since mobility between RCAF nodes isexpected to be rather infrequent.

In the proposed solution, the PCRF 100 and RCAF 200 observe thefollowing rules. PCRF rules:

-   -   The PCRF 100 maintains the current RCAF 200 which has last        indicated that the UE is affected by congestion.    -   When a new RCAF indicates that the UE is affected by congestion,        the PCRF 100 sends a message to the old RCAF to explicitly        release context at the old RCAF.    -   When the PCRF 100 receives a message from a new RCAF that does        not indicate that the UE is affected by congestion, that message        is not taken into account at PCRF 100. Such a message may be a        message indicating the “no congestion” state for the UE, or a        message indicating a set of congestion levels for the UE which        includes the “no congestion” state in case reporting        restrictions are used. When receiving such a message, the        current RCAF remains unchanged; no release context message is        sent to the old RCAF, and the PCRF 100 assumes the previous        congestion status without updating it to no congestion state.        However, the message may be acknowledged towards the RCAF.    -   When PCRF 100 removes its own UE context at IP-CAN session        termination (e.g., UE is being detached), then PCRF explicitly        signals to the current RCAF to releases context the UE context.

RCAF rules:

-   -   When indicated by PCRF signaling, an RCAF releases the UE        context, including any dynamic reporting policy. This also        implies that the RCAF does not indicate to the PCRF that the        congestion state is over.

Note that if UE becomes affected by congestion again after the UEcontext has been released, the RCAF 200 reports change to congestionstate to PCRF 100 as normally.

FIG. 4 shows an example of a mobility handling from a first RCAF, RCAF1named hereinafter, to a second RCAF, named RCAF2 hereinafter. In FIG. 4RCAF1 has the reference number 200 a and RCAF2 has the reference number200 b. In step S41, RCAF1 200 a report a congestion level A to the PCRF100, the PCRF 100 acknowledging the congestion information to the RCAF1200 a in step S42. In step S43, the PCRF 100 stores the current RCAF,here RCAF1 200 a, as the congestion monitoring unit which monitors thecongestion state of the mobile entity in question. To this end, the PCRF100 can have a database in which the different congestion monitoringunits which currently report the congestion states per UE are stored. Instep S44, a second RCAF 200 b reports the congestion level, in step S45,the PCRF 100 acknowledging the received congestion information. In stepS46, the new RCAF 200 b then replaces the formerly stored RCAF1 200 a inthe database list (S46). The PCRF 100 then transmits a release messageto the old RCAF1 200 a which is acknowledged in step S48 and the contextinformation is released in step S49 at the old RCAF1 200 a.

In FIG. 5, the embodiment is shown where the PCRF 100 determines that adata packet session of the UE ended. In step S51, the PCRF 100determines the IP CAN session termination. In step S52, a releasemessage is transmitted to the RCAF 200, the RCAF being the RCAF that iscurrently stored in the list at the PCRF 100. The RCAF 200 acknowledgedthe received message in step S53 and the context is released in stepS54.

In the embodiment of FIG. 4, the release context message in step S47ensures that the RCAF1 200 a does not send any subsequent messagesindicating a non-congested state at RCAF1 200 a. It may happen that theRCAF1 200 a still sends a message indicating no congestion state beforeit receives the release context message. However, such a non-congestionindication from RCAF1 200 a is not taken into account at the PCRF 100based on the above-mentioned rules.

In the case of FIG. 5, the release context message to the RCAF 200ensures that the RCAF 200 signals to the PCRF 100 once again should themobile entity move back to the RCAF 200 and is affected by congestion.

The use of the release context messages also makes sure that possiblereporting restrictions which are stored as part of the release contextin the RCAF cannot become obsolete. This is ensured because each timethe UE moves to a RCAF and terminates its session, the old reportingrestriction is removed.

FIGS. 2 and 3 illustrate exemplary structures of a PCRF 100 or an RCAF200. Making reference especially to FIG. 2, the PCRF 100 contains aninput/output unit 110 with a transmitter 111 and a receiver 112. Thetransmitter 111 symbolizes the possibility of the PCRF 100 to transmitdata to other entities, the receiver 113 receiving data from otherentities. The input/output unit 110 is used for communication with anyof the other entities such as the RCAF 200, PDN gateway 40, the TDF 50or the PDN 60. The PCRF 100 comprises a database 130 in which theinformation can be stored which RCAF is reporting congestion states forwhich mobile entity. As discussed above, the PCRF 100 stores the currentcongestion monitoring unit or RCAF and if a congested state is receivedfrom another RCAF, the currently stored RCAF is replaced by the new RCAFthat reported a congested state. However, as discussed above the RCAF isonly stored when the new RCAF reports a congested state and not anon-congested state. A processing unit 120 is provided comprising one ormore processors which is responsible for the operation of the PCRF 100.The processing unit can generate the commands that are needed to carryout the above discussed procedures in which the PCRF 100 is involved. Amemory 140 is provided which may be a read-only memory, a flashread-only memory, a random access memory, a mass storage, a hard disk orthe like. The memory 140 includes suitable program codes to be executedby the processing unit 120 so as to implement the above-describedfunctionalities.

In the same way, the RCAF 200 shown in FIG. 3 comprises an input/outputunit 210 for communicating with other entities, inter alia the entitiesshown in FIG. 1, the input output unit comprising a transmitter 211 anda receiver 212. The transmitter 211 is used for the transmission of datato other entities, the receiver being used to receive data from otherentities. A processing unit 220 including one or more processors isprovided which is used for the operation of the RCAF 200. The processingunit 220 is adapted to initiate the functions discussed above in whichthe RCAF 200 is involved. A memory 230 is provided which can beread-only memory, a flash read-only memory, a random access memory, amass storage, a hard disk or the like and the memory 230 includes asuitable program code to be executed by the processing unit 220 so as toimplement the above-described functionalities. The memory mayfurthermore store, on a per UE base reporting restrictions as discussedin more detail below.

It should be understood that the structures shown in FIGS. 2 and 3 aremerely schematic and that the PCRF 100 or the RCAF 200 may actuallyinclude further components which for the sake of clarity have not beenillustrated.

It should also be understood that the different entities shown in FIGS.2 and 3 need not be incorporated by several entities. Furthermore, thedifferent entities shown in FIGS. 2 and 3 may be incorporated byhardware or software or a combination of hardware and software.

FIG. 6 summarizes some of the steps carried out at PCRF 100. In stepS61, a congestion information is received from one of the RCAF and instep S62, the RCAF from which the congestion information or indicationis received is stored as the current congestion monitoring unit/RCAF. Ifin step S63 a congestion information is received from another RCAF 200,the currently stored congestion monitoring unit/RCAF is informed torelease congestion information relating to the mobile entity inquestion.

In FIG. 7, another embodiment is shown where the PCRF first receivesinformation about a congested state and then receives information abouta non-congested state. In step S71 and S72, information about acongested state is received from one of the RCAFs 200 and the RCAF fromwhich the information is received is stored as it was discussed above inconnection with steps S61 and S62.

In step S73, the PCRF now receives an indication of a non-congestedstate by another RCAF. The PCRF can acknowledge this message to the RCAFfor which the information about the non-congested state is received(step S74) but the PCRF ignores this information and does not amend thecurrently stored congestion monitoring unit (at step S75).

FIG. 8 summarizes steps carried out at the RCAF 200. When an RCAFreceives an indication to release a congestion information or contextmobile entity in step S81, the congestion information or context isrelease in step S82 as instructed by the PCRF.

In the following, a possibility to release a context is described inmore detail.

It is possible to avoid the Release context message from the PCRF 100 tothe RCAF 200 in case the last reported congestion level is “nocongestion” and the PCRF 100 has not installed any reportingrestrictions into the RCAF 200. This is because in this case, there isno risk with an obsolete UE context at the RCAF 200, since the UEcontext would be “empty” for such a UE. Hence, in this case, the RCAF200 can release the UE context on its own based on a timer.

However, for this optimization the PCRF 100 needs to use a guard timerto avoid mobility back to the original RCAF 200 for a short period oftime. That is needed to handle cases when the UE has become affected bycongestion at the old RCAF just before moving to a new RCAF. In thatcase the PCRF 100 could receive a congestion indication from the oldRCAF as well. In this optimization, such a congestion indication needsto be responded by a Release context message

In the following, a situation is discussed where the network comprisesseveral PCRFs 100.

It is possible for a UE to be connected to multiple PDNs (Packet DataNetworks) identified by different APNs (Access Point Name). In thatcase, the PCRF 100 corresponding to these different PDN connections (PDPcontexts) can be different.

Such multiple PCRF case can be simply handled in such a way that each Npconnection to a PCRF 100 is handled independently. The Np mobilityapproach presented above applies for each Np connection to a PCRF 100.The UE context in the RCAF 200 in this case can be handled separatelyfor each Np connection. A Release context message from a PCRF applies tothe UE context specific to the given Np connection only.

As an optimization, it is possible to realize an embodiment withcombined handling in a way that a release context message from one PCRF100 also releases the context corresponding to all other Np connectionsto other PCRFs. Such optimization could make it faster to release thefull context in the RCAF 200.

In the following, a situation is discussed where a mobile entityfrequently moves from one area covered by one RCAF to another areacovered by another RCAF.

In case of a UE which is located at the borderline between the area oftwo RCAFs, it may happen that there is frequent mobility between RCAF1and RCAF2 as a UE moves back and forth between their areas. This mayhappen e.g., when RCAF1 and RCAF2 correspond to different RATs (one ise.g. for 3G, the other is for LTE), and the UE is moving around theborder of the coverage area of one of the RATs. In this case, thesolution may lead to frequent signaling due to the frequent contextrelease at the old RCAF.

When the PCRF detects frequent mobility for a given UE, it is possibleto send an indication to the RCAF to use a longer reporting period inorder to reduce the signaling. Such indication can be sent to thecurrent RCAF (and after mobility, to the other RCAF which becomescurrent). Even though this leads to lower accuracy in the PCRF, such anapproach can limit the signaling load.

The indications or messages described above that are exchanged betweenthe PCRF 100 and the RCAF 200 an be incorporated as a single message.However, the indication can also be incorporated into another message.

Summarizing, the above-described invention allows a reduction of thesignaling between a RCAF 200 and PCRF 100 due to the fact that onlychanges in the congestion state are reported. Furthermore, the inventioncan be used to provide an accurate information in the PCRF since changesin the congestion state are reported without waiting for a validitytimer to expire. The invention furthermore can be used to guarantee thateven during UE mobility, the information in the PCRF 100 will beconsistent with the congestion situation experienced by the UE.Furthermore, the invention can be used to guarantee that any obsoletecontext information stored in a RCAF is removed.

The invention claimed is:
 1. A method, by a policy control unit of amobile communications network, to control a signaling of congestioninformation of mobile entities at a plurality of congestion monitoringunits that monitor which mobile entities are affected by a congestionstate in a radio access network of the mobile communications network,the method comprising: receiving, from one of the congestion monitoringunits, an indication that one of the mobile entities is affected by acongestion state; storing said one congestion monitoring unit from whichthe indication is received as the current congestion monitoring unit forsaid one mobile entity; receiving, from another congestion monitoringunit, the indication that said one mobile entity is affected by acongestion state; and indicating, in response to the indication receivedfrom the other monitoring unit, to the current congestion monitoringunit a release of congestion information relating to said one mobileentity.
 2. The method of claim 1 wherein, when a second indication isreceived from any of the plurality of congestion monitoring units thatsaid one mobile entity is not affected by a congestion state, the secondindication is ignored and no indication is sent to the currentcongestion monitoring unit to release congestion information.
 3. Themethod of claim 2, wherein the stored current congestion monitoring unitis kept as the current congestion monitoring unit when the secondindication is received from any of the plurality of the congestionmonitoring units.
 4. The method of claim 2, wherein an acknowledgementis transmitted as a response to the congestion monitoring unit whichtransmitted the second indication.
 5. The method of claim 1, wherein theother congestion monitoring unit is stored as the current congestionmonitoring unit when said other congestion monitoring unit has indicatedthat said one mobile entity is affected by a congestion state.
 6. Themethod of claim 1, wherein, when a termination of a data packet sessionof the said one mobile entity is detected, it is indicated to thecurrent congestion monitoring unit to release congestion informationrelating to said mobile entity.
 7. The method of claim 1, whereinindicating a release of congestion information comprises information torelease a context for said one mobile entity.
 8. The method of claim 1,further comprising informing the plurality of congestion monitoringunits whether or not a monitoring of the congestion state should becarried out for said one mobile entity.
 9. The method of claim 8,wherein, if the monitoring of the congestion state should be carriedout, the plurality of congestion monitoring units are informed that thecongestion state should only be reported to the policy control unit whenthe congestion state has reached a predefined level or a predefinedlevel range.
 10. A policy control unit configured to control a signalingof congestion information of mobile entities at a plurality ofcongestion monitoring units that monitor which mobile entities areaffected by a congestion state in a radio access network of the mobilecommunications network, the policy control unit comprising: a receiverconfigured to receive, from one of the congestion monitoring units, afirst indication that one of the mobile entities is affected by acongestion state; a database configured to store said one congestionmonitoring unit from which the first indication is received as thecurrent congestion monitoring unit for said one mobile entity; atransmitter; and a processing circuit; wherein the processing circuit isconfigured to use the transmitter to indicate to the current congestionmonitoring unit to release congestion information relating to said onemobile entity in response to the received first indication, when thereceiver receives the first indication that said one mobile entity isaffected by a congestion state from another congestion monitoring unit.11. The policy control unit of claim 10, wherein the policy control unitis a Policy and Charging Rules Function (PCRF).
 12. A method to operatea congestion monitoring unit that monitors which mobile entities areaffected by a congestion state in a radio access network of a mobilecommunications network, the method comprising: sending, to a policycontrol unit of the mobile communications network, an indication thatone of the mobile entities is affected by a congestion state; receiving,from the policy control unit of the mobile communications network, anindication to release congestion information relating to said one mobileentity; and releasing the congestion information for said one mobileentity in response to the received indication.
 13. The method of claim12, further receiving mobile entity dependent information whether amonitoring of the congestion state should be carried out for thecorresponding mobile entity or not, wherein a monitoring of a congestionstate is only carried out for one of the mobile entities if thecorresponding mobile entity dependent information states that themonitoring of the congestion state should be carried out.
 14. The methodof claim 13, wherein the mobile entity dependent information containsthe information that a congested state is present for one mobile entitywhen the congestion state has reached a predefined level or a predefinedlevel range, wherein the indication that said one mobile entity isaffected by a congestion state is only transmitted to the policy controlunit when the congestion state has reached the predefined level or levelrange.
 15. A congestion monitoring unit configured to monitor whichmobile entities are affected by a congestion state in a radio accessnetwork of a mobile communications network, the congestion monitoringunit comprising: a transmitter configured to send, to a policy controlunit of the mobile communications network, an indication that one of themobile entities is affected by a congestion state, a receiver configuredto receive, from the policy control unit of the mobile communicationsnetwork, an indication to release congestion information relating tosaid one mobile entity, and a processing circuit configured to releasethe congestion information for said one mobile entity in response to thereceived indication.
 16. The congestion monitoring unit of claim 15,wherein the congestion monitoring unit is a Radio Access NetworkCongestion Awareness Function (RCAF).
 17. A non-transitorycomputer-readable medium comprising, stored thereupon, a computerprogram comprising instructions that, when executed by at least oneprocessing circuit in a policy control unit of a mobile communicationsnetwork, cause the at least one processing circuit to control asignaling of congestion information of mobile entities at a plurality ofcongestion monitoring units that monitor which mobile entities areaffected by a congestion state in a radio access network of the mobilecommunications network by: receiving, from one of the congestionmonitoring units, an indication that one of the mobile entities isaffected by a congestion state; storing said one congestion monitoringunit from which the indication is received as the current congestionmonitoring unit for said one mobile entity; receiving, from anothercongestion monitoring unit, the indication that said one mobile entityis affected by a congestion state; and indicating, in response to theindication received from the other monitoring unit, to the currentcongestion monitoring unit a release of congestion information relatingto said one mobile entity.
 18. A non-transitory computer-readable mediumcomprising, stored thereupon, a computer program comprising instructionsthat, when executed by at least one processing circuit in a congestionmonitoring unit that monitors which mobile entities are affected by acongestion state in a radio access network of a mobile communicationsnetwork, cause the at least one processing circuit to: send, to a policycontrol unit of the mobile communications network, an indication thatone of the mobile entities is affected by a congestion state; receivefrom the policy control unit of the mobile communications network, anindication to release congestion information relating to said one mobileentity; and release the congestion information for said one mobileentity in response to the received indication.